That magnaflow H looks like its good quality, & I know for a fact that their cats a great quality. Catted H pipes are pretty rare nowadays, & I'm not sure if Mac still makes 1 for a fox? I will tell you this though, Mac uses cheap catco converters on there catted midpipes. I installed a brand new Mac catted H pipe (for longtubes) on my Mach 1, & even with it being brand new, the car barely passed the sniffer. Im not bashing Mac, they make some good exhaust parts & I run their exhaust on both of my stangs, but the cats they use are garbage. I would either get the Magnaflow H, or buy a set of magnaflow converters & have them welded into an o/r H.
Well, if there is no sniffer, I would get the cheapest 2 1/2" cats you could find, gut em out, & then weld em' in. No point on corking up your exhaust if you don't have to, unless you want a quieter tone...
I dunno, but I figure the tone would be the same. What mufflers are you running & have you ever had an catless exhaust on your car before? Cats mellow out the tone quite a bit...